CHAPTER XX 

 HEMISPHAERIALES 



With the Hemisphaeriales, we have left the classic Pyrenomycetes 

 and passed to the Discomycetes. As their name signifies, the Hemi- 

 sphaeriales form a group of families which originally were included in the 

 Sphaeriales (including Perisporiales and Hysteriales), but have been 

 removed to a new order on account of their disciform, pseudosphaerial 

 fructification whose scutellate cap, with a peculiar, generally radial 

 structure but lacking an ostiole, ruptures irregularly. They are inter- 

 mediate between the Pyrenomycetes and the Phacidiales. The Hemi- 

 sphaeriales are a temporary, artificial order, containing a series of generally 

 parasitic families. 



Stigmateaceae. — This family is distinguished by the subcuticular 

 position of the fructification, as in the Trabutieae. Stigmatea Robertiani 

 (Hormotheca Robertiani) on Geranium Robertianum (Theissen, 1916; 

 Theissen and Sydow, 1917; Klebahn, 1918; Killian, 1922) appears on 

 the leaves of the host, in damp weather in summer and fall, in the form 

 of small spots up to 3 mm. across. It continues to develop through the 

 winter. The mycelium lives only on the outer surface of the infected 

 leaves, generally on the upper surface, occasionally on the lower surface, 

 often on both. Between epidermis and cuticle, it forms a continuous 

 membranous layer which neither penetrates the deeper tissues by hyphae 

 nor the epidermal cells by haustoria (Fig. 194, 1). In the central part, it 

 gradually thickens into a flat plectenchymatous cushion in whose interior 

 there appear two deeply staining uninucleate cells, in one or several 

 neighboring positions, without conidial production (Fig. 194, 2). Gen- 

 erally only one develops while the other is resorbed. This one cell goes 

 through several nuclear divisions, elongates and develops, by the forma- 

 tion of several septa, into a slightly bent, fertile hypha (Fig. 194, 3). 

 Its innermost cell, i.e., that which lies next the middle of the plecten- 

 chyma, elongates again perpendicular to the leaf surface and develops 

 to a binucleate ascogonium with a peculiar receptive process at its tip 

 (Fig. 195, 1). Another cell of the fertile hypha develops to a binucleate 

 antheridium. The two organs come in open communication with each 

 other, the male nucleus migrates to the ascogonium (Fig. 195, 2), after 

 repeated division unites with the female nucleus and migrates into the 

 ascogenous hyphae which later proceeds to the formation of asci between 



true paraphyses. 



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